1. Field of the Invention
The present invention relates to measurement of flow rate of a purge gas flowing into a carrier such as a FOUP in which semiconductor wafers or the like are housed.
2. Description of the Related Art
When articles such as semiconductor wafers or reticles are housed and stored in a carrier such as a FOUP or a reticle pod, a purge gas such as a nitrogen gas or clean dry air is supplied to the carrier in order to prevent contamination, oxidation, and the like of the wafers or the like. Specifically, the purge gas supply line is provided in a stocker, an automated warehouse, and the like in which the carrier is stored, and a nozzle of the supply line and a gas introduction section of the carrier are connected to each other so that the purge gas is introduced into the carrier. A valve of the gas introduction section is configured to open when the gas introduction section is set to the nozzle of the purge gas supply line, and to close when the carrier is removed. In this technique, it is necessary to manage the flow rate of a gas introduced into the carrier. For example, a variation in the state of the supply line, specifically, a variation in blockage of members such as pipes, in-line filters, and the like, a variation in length of the pipes, a variation in operation pressure of the nozzles, a variation in airtightness at connection portions of the carrier and the supply line, or the like cause a problem. The connection portions of the carrier and the gas introduction section are portions constituted by, for example, the nozzle and the gas introduction section, and airtightness therebetween is maintained by the weight of the carrier itself.
The inventors proposed to transport a measurement device including a flowmeter using a transport device provided in a stocker and measure a flow rate of the purge gas at each cell. See, for example, JP4670808B.
When a measurement device is provided with a flowmeter, a power supply, and the like in order to measure the flow rate of the purge gas, the measurement device weighs more than a carrier in which only one wafer is housed. Because the carrier in which only one wafer is housed is light-weight, airtightness between a nozzle and a gas introduction section is insufficient and the purge gas is likely to leak. Accordingly, if a measurement device appropriate for a carrier in which an average number of wafers are housed is used to measure the flow rate, only the flow rate under a favorable condition will be managed. The same problem occurs in the case where another type of articles such as reticles are housed.